We report on eight years of spectropolarimetric monitoring of the WR140 binary. The broad-band linear polarization decreased systematically after the 1985 periastron passage. By 1991, it settled to a constant value at which it has remained through the 1993 periastron passage. We do not detect, in data taken after 1989, a line-effect in He II Λ4686. This suggests either that the continuum and the line emission scatter at the same region, or that any intrinsic polarization has been below our detection limit. We conclude that the presently observed polarization of WR140 is consistent with interstellar foreground polarization.

Ultraviolet high-resolution SWP images of the binary system WR140 (HD 193793, WC7+O4-5) were taken with IUE over the period 1979 — 1993. This poster presents a radial-velocity study of the absorption lines, attributed to the O-type component, applying the infrared period of P = 2900 days.

We present the first results of the IUE monitoring campaign of the WC7+O4-5 binary system WR140. Thirty-four high-resolution short-wavelength spectra were obtained in 1979—93, i.e., over more than one orbital period of 7.9 yr. The spectra show variations in the strong resonance lines of CIV and SiIV: large variations occur at the blue edges of the absorption parts of their P-Cygni profiles just after periastron passage. The observed profile changes are discussed in terms of a velocity variation at periastron passage and/or turbulence in the sightline to the O4—5 star at this time.

New observations of the colliding wind Wolf-Rayet WC7+O4-5 binary WR140 (HD 193793) at 6 cm and 21 cm with the Westerbork Synthesis Radio Telescope are presented. They show that the 21 cm flux, in particular, rose to a sharp maximum in 1992, lagging about a year behind the 6 cm flux. After maximum, both fell simultaneously. The data are interpreted in terms of the varying circumstellar extinction to a non-thermal source in the wind interaction region due to the winds of both WC and O stars.

The presence of heated circumstellar dust around WC type Wolf-Rayet stars is reviewed in terms of the episodic or persistent condensation of carbon grains in their stellar winds. At present, 19 WC stars are known to form dust persistently and 7 episodically. Infrared spectroscopy suggests that the grains are amorphous rather than graphitic carbon. The properties of the stars which make dust episodically are reviewed in terms of processes in colliding winds in WR binary systems and the possible applicability of these processes to the stars which make dust persistently in examined.